1. Field of the Invention
The invention relates to a clamping device for rotating tools, and in particular to a clamping device that increases related runout accuracy and durability.
2. Technical Background
It is common knowledge that rotating tools, such as drills and especially milling tools, can be held in the clamping device of a machine tool. Such clamping devices, especially so-called ER collet chucks according to ISO 15488, comprise a base, which has a coupling-side end for mounting in a machine tool and a tool-side end, which has a mounting hole which is centric with the axis of the tool and into which a tool shank can be axially inserted from the front end of the tool-side end of the base; a collet chuck which surrounds the shank and is arranged so as to be axially displaceable in the mounting hole and whose outer sleeve has a section which essentially tapers conically from the front end of the base, the outer sleeve supporting itself on a matching tapering conical section of the inner sleeve of the mounting hole; and, a locknut which has an internal thread that engages with an external thread of the base and which forces the collet chuck into the mounting hole axially, relative to the mounting hole. Inserted by its cylindrical shaft into the collet chuck, the tool is clamped radially when the locknut, and on being tightened, forces the collet chuck into the mounting hole and thereby reduces the inner diameter of the collet chuck. The compressibility of the collet chuck is provided by slots penetrating the collet chuck radially.
Known ER collet chucks are very versatile. On account of their generous slot widths, the collets of these ER collet chucks cover a relatively large clamping range in the order of approximately 1 mm, i.e., a clamping device with a mount for tools having a shank diameter of 10 mm can also clamp shank diameters of 9 mm. This is achieved by the fact that, in the case of smaller shank diameters, the collet chuck is forced further into the mounting hole of the base and so closes further in the context of the compressibility afforded by the slots.
The disadvantage of this clamping device, however, is that the chuck has radial support only over a relatively short axial range of the mounting hole. As a result, both the runout accuracy and the rigidity of the clamped tool deteriorate. If, in addition, the insertion depth of the tool shank is less than the axial expansion of the collet chuck, there are areas on the inside of the collet chuck where the tool shank does not make contact. Since, in this area, the clamping force of the collet chuck is not cushioned by the tool shank through support, it can happen that the wall of the collet chuck curves and/or the collet chuck in the mounting hole cants. This reduces not only the runout accuracy as well, but can lead to damage of the collet chuck and base.
The object of the present invention is to eliminate these drawbacks of hitherto conventional clamping devices of this type and thus to increase the runout accuracy and the durability of the clamping device.